Existing mould opening and closing mechanisms for use in opening and closing three moulds simultaneously by moving a portion of each mould relative to further portions of that mould comprise three mould portion supports each arranged to support a portion of a mould, three levers each of which is pivotal on a fixed pivot and each of which is pivotally connected to one of the mould portion supports, and moving means connected to the levers and operable to cause the levers to pivot about the fixed pivots so that the mould portion supports are moved and the mould portions are moved away from or towards further mould portions thereby opening or closing the moulds. It is desirable that such a mechanism should operate rapidly and accurately and should close the three moulds with substantially equal pressures. However, the problem of providing substantially equal closing pressures to three moulds with rapidly and accurately operating mechanism as hitherto only been solved partially.